Definition
The tendency of a rotating mass to resist changes in its rotational speed because of its stored kinetic energy. In aviation, the term describes how spinning components such as propellers, rotors, turbine wheels, and engine crankshafts smooth out fluctuations in power and continue rotating briefly after the driving force is removed.
Plain English
Once something heavy is spinning, it doesn't want to speed up or slow down quickly. It keeps turning steadily on its own for a while, even if the push driving it changes or stops.
Context Anchor
Seen in piston-engine and propeller discussions, especially when explaining engine smoothness and how quickly engine speed changes after a power change.
Derivation
Named after the flywheel — a heavy wheel deliberately added to engines to even out the power pulses from each cylinder firing. The wheel's mass stores energy on the power stroke and releases it between strokes, keeping rotation smooth.
Why Pilots Care
Affects engine smoothness, starting reliability, shutdown behavior, and continued propeller rotation after power loss.
Analogy
Like a bicycle wheel spun by hand: once it's going, it keeps turning on its own for a while, and small pushes or drags barely change its speed.
Intuition Check
Do not assume flywheel effect always means there is a separate flywheel installed. In aviation use, the effect can come from any significant rotating mass, including the propeller.
Example Sentence 1
The flywheel effect of the propeller kept it turning for several seconds after the magnetos were switched off.
Example Sentence 2
After an engine failure the flywheel effect allows the propeller to keep windmilling until the pilot secures it.